Transient free radicals in iron/oxygen reconstitution of mutant protein R2 Y122F. Possible participants in electron transfer chains in ribonucleotide reductase.

摘要: Ferrous iron/oxygen reconstitution of the mutant R2 apoprotein Y122F leads to formation a diferric center similar that wild-type protein Escherichia coli ribonucleotide reductase. This reaction requires two extra electrons, supplied or transferred by matrix R2. We observed several transient free radical species using stopped flow and freeze quench EPR UV-visible spectroscopy. Three radicals occur in time window 0.1-2 s, i.e. concomitant with site. They include strongly iron-coupled (singlet signal) only at < = 77 K, singlet signal room temperature, Tyr-356 (light absorption 410 nm), an invariant residue proposed be part electron transfer chain catalysis. additional are 6 s 20 min. Two these conclusively identified, specific deuteration, as tryptophan radicals. Comparing side geometry distance iron characteristics radicals, we propose certain Trp residues likely harbor